Question

Strong heating of ferrous sulphate leads to the formation of a brown solid and two gases. This question can be categorized as:
(A) displacement and redox.
(B) decomposition and redox.
(C) displacement and endothermic.
(D) decomposition and exothermic.

Answer 1

The chemical reaction for strong heating of ferrous sulphate is written as: $2FeS{{O}_{4}}(s)\to F{{e}_{2}}{{O}_{3}}(s)+S{{O}_{2}}(g)+S{{O}_{3}}(g)$. Also, look at the change in oxidation numbers of Fe and S during the chemical reaction.

Complete solution:
> As we already know that Ferrous sulphate crystals contain 7 water molecules $(FeS{{O}_{4}}.7{{H}_{2}}O)$ which on heating, lose water and anhydrous ferrous sulphate $(FeS{{O}_{4}})$ is formed. As a result of which the colour changes from light green to white. On heating further, anhydrous ferrous sulphate decomposes and form ferric oxide ($F{{e}_{2}}{{O}_{3}}(s)$) which is a brown colored solid, sulphur dioxide ($S{{O}_{2}}(g)$) and sulphur trioxide ($S{{O}_{3}}(g)$). So, the gas emitted smells like burning sulphur.
$2FeS{{O}_{4}}(s)\to F{{e}_{2}}{{O}_{3}}(s)+S{{O}_{2}}(g)+S{{O}_{3}}(g)$
> It is evident from the reaction that the single reactant $(FeS{{O}_{4}})$ decomposes to form three different products. Therefore, the reaction is a decomposition reaction.
Also, the oxidation number of iron changes from +2 in $FeS{{O}_{4}}$ to +3 in$F{{e}_{2}}{{O}_{3}}$ causing oxidation and the oxidation state of S changes from +6 in $FeS{{O}_{4}}$ to +4 in $S{{O}_{2}}$ causing reduction. Since, Fe(II) is oxidized to Fe(III) and S (VI) is reduced to S (IV) , it is a redox reaction. A reduction-oxidation (redox) reaction is a type of chemical reaction which involves a transfer of electrons between two chemical species.

So, the answer is option (A).

Additional information:

A displacement reaction is the one in which the atom, or a set of atoms, is displaced by another atom or set of atoms, in a molecule.
Exothermic reactions are reactions that release energy, generally in the form of heat or light. On the other hand endothermic reactions are reactions that require external energy, usually in the form of heat, for the reaction to occur and hence tend to cause their environments to cool down.

Note: Ferrous is different from ferric though both are forms of iron. Ferrous is $F{{e}^{2+}}$ where iron loses 2 electrons while ferric is $F{{e}^{3+}}$ wherein iron loses 3 electrons.